1. Field of the Invention
The present invention relates to a highly antioxidant resin composition. More particularly, the present invention relates to a highly antioxidant resin composition comprising a resin, a heat stabilizer and a hindered amine base weathering stabilizer and having good heat stability and weather resistance.
2. Description of the Related Art
The amount of resins which are used outdoors is increasing year by year. Such outdoor use resins are required to have weather resistance properties according to their application. To this end, various weathering stabilizers have been developed. Recently, hindered amine base weathering stabilizers, which are so-called hindered amine light stabilizers (HALS) are often used, since they can prevent decrease of the mechanical properties or change of color tone of the resin compositions when subjected to outdoor weathering much better than the conventional weathering stabilizers (cf. Japanese Patent Kokai Publication No. 86645/1984).
Since the weathering stabilizer cannot impart processing stability or heat stability to the resins, a heat stabilizer (e.g. hindered phenol base heat stabilizers, sulfur base heat stabilizers and phosphite ester base heat stabilizers) is generally added to the resin composition.
However, under certain conditions, the resin composition containing both the heat stabilizer and the hindered amine base weathering stabilizer may suffer from deterioration due to poor heat stability such as gellation or seizure during processing or discoloration after processing. Further, when exposed to the outdoor atmosphere, the resin composition may be degraded due to poor weather resistance such as a decrease of mechanical properties or changes of gloss or color tone. Accordingly, the conventional resin compositions are not satisfactory in both the heat stability and the weather resistance. Though the heat stability and the weather resistance may be improved to some extent by the addition of larger amounts of the heat stabilizer and the hindered amine base weathering stabilizer to the resin, the resin composition may be yellowed, or the heat stabilizer and/or the hindered amine base weathering stabilizer may bleed out on the surface so that the appearance of a molded article is deteriorated.
In particular, it is known that, when the hindered phenol base heat stabilizer and the hindered amine base weathering stabilizer are used in combination, the hindered phenol base heat stabilizer causes yellowing of the resin and the hindered amine base weathering stabilizer interferes with the antioxidant action of the hindered phenol base heat stabilizer.